Thermally-bonded polyester fiber batts are described in my parent U.S. Pat. No. 4,794,038 (and in many other documents, including, e.g., U.S. Pat. Nos. 4,668,562 and 4,753,693, and WO 88/00258, corresponding to Ser. No. 880,276, filed June 30, 1986), and such batts have gained large scale commercial use, particularly in Europe and Japan. Binder fibers can be intimately blended into the load-bearing polyester fiber to achieve true "through bonding" of the polyester fiber when they are suitably activated. "Through bonding" has provided higher support and better durability than resin-bonding of polyester fiber, which was the conventional method, and can also provide reduced flammability than conventional resin-bonding. Binder fiber blends are now used on a large scale to make batts in furnishing, mattresses and similar end uses where a high support and good durability are required. They have, however, seldom been used as the only filling material in these end uses, but the common practice is to use the polyester fiber batts as a "wrapping" around a foam core. It is believed that the main reason is that it has been difficult to achieve the desired properties without using the foam core. To achieve the desired resilience and durability, bonded fiber batts would have to reach high densities, in the 35 to 50 kg/m.sup.3 range. Such high densities could not be achieved commercially until very recently. Even then, such condensed (i.e. high density) batts as have appeared on the market in Europe and the U.S. (e.g., in 1987) have been nonuniform in density, lower layers being denser than upper layers, which results in increased loss of height during use. These high density "block batts" (as they have been referred to) have also been characterized by relatively poor conformation to a user's body. I believe that this results from their structure, since the batts are made from a series of superposed parallel layers; when these parallelized structures are deformed under pressure, they tend to pull in the sides of the whole structure rather than to deform more locally, i.e., to conform to the shape and weight of the user's body, as would latex or good quality polyurethane foam.
Thus, hitherto, the performance of existing "block batts" made wholly from bonded polyester fiber has not been entirely satisfactory. The difficulty has been how to combine in one structure both durability and comformability to a human body. To obtain durability, with existing "block batts" from superposed carded webs, one has had to increase the density until one obtains a structure that does not conform as comfortably as other structures, i.e. not wholly from bonded polyester fiber. I have now solved this problem according to the present invention.
As will be apparent hereinafter, an essential element of the solution to this problem (i.e. of the present invention) is to use a binder fiber blend in a 3-dimensional form, as fiberballs, rather than as flat webs or as a formless mass of fibers. This may seem surprising, but the advantages will be explained, hereinafter. Preferred fiberballs (and their preparation and bonding) are the subject of my parent U.S. Pat. No. 4,794,038, referred to above, the disclosure of which is hereby incorporated by reference, it being understood, however, that other fiberballs may be used in the present invention, as indicated later herein.